Technical Field
The present disclosure pertains to vehicles capable of flight and, more particularly, to manned and unmanned vehicles having combined methods of lift, including dynamic lift and displacement buoyancy.
Description of the Related Art
Aircraft are vehicles that are capable of flight and include lighter-than-air aircraft, which can rise and remain suspended by using contained gas weighing less than the air that is displaced by the gas, as well as heavier-than-air aircraft, such as fixed and movable wing airplanes, which use dynamic lift created by movement of a wing through the air and rotary wing craft such as helicopters. Each type of aircraft has its own advantages and disadvantages.
In an effort to utilize the advantages of different modes of lift, proposals have been made for combining wings with lighter-than-air aircraft. For example, U.S. Pat. No. 6,311,925 describes an airship and method for transporting cargo having a supporting structure in the airship envelope that has attached thereto the airfoils or wings, which extend outward from the airship. This design attempts to avoid the structural limitations of having loaded wings exerting force directly on the airship envelope. Although jet-assisted turboprop engines are used on the wings, this design makes inefficient use of both forms of lift taken together and in combination with the turboprop engine. Moreover, this design does not utilize the vertical takeoff or landing (VTOL) capabilities of fixed wing aircraft, in part because the envelope is designed to provide sufficient lift to overcome the weight of the aircraft; i.e., it has a positive hydrostatic buoyancy.
One disadvantage of having positive hydrostatic buoyancy is the difficulty of controlling the lighter-than-air aircraft on or near the ground in windy conditions. Another disadvantage is that such vehicles must have large drag-inducing profiles in order to hold sufficient gas to provide the necessary static lift. Moreover, the forward speed of this design is limited to generally 50 knots or less.
Hence, there is a need for an aircraft that can combine hydrostatic buoyancy with aerodynamic lift in which increase airspeed is achievable without unduly stressing the envelope and that provides increased dynamic control in windy conditions and maneuverability near the ground. In addition, such a craft should provide safe engine-out performance to ensure cargo and passengers are unharmed in the event of an engine-out descent.